My son's levels dropped below all the time his first year, since then they have been fine, but as a baby they where always so low, it is because they are going through growth spurts all the time He is doing great now and i dont know if it is related at all but he has a high phe tolerance. My older daughter never dropped below 0 and she is 7 now and her 3 year old brother gets more than double the amount of phe she gets.